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Rocky Mountain Spotted Fever In Arizona
CAPT Jennifer McQuiston, DVM, MS, dACVPMVeterinary Epidemiologist
Rickettsial Zoonoses BranchCenters for Disease Control and Prevention
Rocky Mountain Spotted Fever (RMSF)
Rickettsia rickettsii, tick-borne pathogen
Acute presentation: Fever, headache, rash (humans)
Rapidly progressive disease with respiratory, gastrointestinal, and neurologic manifestations
Multisystem organ failure, death (in 1-10%)
U.S. RMSF Incidence, 2000-2007
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Traditional RMSF Vectors
Dermacentor variabilis
American dog tick
Dermacentor andersoni
Rocky Mountain wood tick
Index Case, 2003
14 month old child died of suspected sepsis following a febrile rash illness
From a tribal community in eastern Arizona
Astute IHS clinician sent samples to CDC for testing
Tested negative for hantavirus, Neisseria meningitidis
PCR positive for R. rickettsii
Index Case, 2003
No history of travel
From same community as the only other AZ RMSF case in the past several years
Environmental investigation:
No Dermacentor spp. of ticks
Heavy household infestation of Rhipicephalus sanguineus (the brown dog tick)
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• Ticks abundant on dogs and in yards of patients’ homes
• > 1,000 ticks collected, all identified as R. sanguineus
• R. sanguineus ticks found attached to 1 confirmed case-patient
Environmental InvestigationReservation #1
Prevalence of R. rickettsii in ticks
Dogs from case homes 30 3 10.0
Stray dogs 46 5 10.9
Case houses (environmental ticks)
275 13 4.7
Non-case houses 273 14 5.1
Sample origin Total
R. rickettsii
PCR +Prevalence (%)
Overall prevalence of R. rickettsii in R. sanguineus ticks: 5.6%
Rhipicephalus sanguineusBrown dog tick
Emerging Vector of RMSF in the United States
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Reservation #1, 2003
Medical chart review with IHS hospital
Enhanced surveillance and testing
More human cases identified
Pediatric serosurvey
Antibodies to spotted fever group rickettsiae detected in 10% of children
Antibodies detected in 16% of children from a neighboring reservation
Reservation #1, 2004
• 13 patients with RMSF were identified from May-September 2004 – 8 confirmed, 5 probable– 10 children ≤12 years of age– 11 hospitalized– 1 death
• All patients had contact with tick-infested dogs
• 4 patients had a history of tick bite preceding illness
RMSF Cases in Eastern AZ, 2003-2011
0
10
20
30
40
50
60
2003 2004 2005 2006 2007 2008 2009 2010 2011
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RMSF in AZ
194 cases 2003-2011
American Indian populations
Expanded to include 4 different reservations
During 2010-2011, > 200X the national RMSF average incidence
15 deaths (case fatality rate 7.7%)
National rate < 0.5%
Pediatric populations significantly impacted
60% children <18 years of age
0
5
10
15
20
25
30
35
40
0-4 5-9 10-19 20-29 30-39 40-49 50-59 60-69 70+
Eastern AZ
U.S.
Proportion of RMSF Cases by Age Group, 2002-2009
Eastern Arizona: 2002-2009 U.S.: 2000-2007 (includes AZ cases)
0
5
10
15
20
25
Eastern AZ
U.S.
Month of RMSF Onset
Eastern Arizona: 2002-2009 U.S.: 2000-2007 (includes AZ cases)
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The Role of Dogs in AZ RMSF
R. sanguineus preferentially feeds on dogs Numerous dogs in the affected area No local animal control or veterinary care Numerous free-roaming dogs Loose definition of ownership
Owned dogs introduce ticks into the home environment, risk for children Role for dogs as a reservoir for R.
rickettsii? New susceptible puppies born each year Amplification among co-feeding ticks
Translocation and potential to expand to neighboring communities?
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Dogs as Sentinels for Human RMSF Risk
• Dogs have heavier exposure to ticks• Dogs develop illness and robust serologic
response to R. rickettsii• Dogs can be systematically sampled more
easily than people • Good indicator of environmental risks• Evidence in dogs precedes first human case
reports – key to action?
Reservation #1 (Eastern AZ)First Human Cases: 2003
Reservation #2 (Eastern AZ)First Human Cases: 2005
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Reservations #1 and #2 Canine Seroprevalence
1996: 5% of dogs were seropositive (n=17/329) 2003-2004, 78% of dogs were
seropositive (n=86/111) Suggests recent emergence in
the affected area since 1996
Reservation #3 (Central AZ)First Human Cases: 2009
Reservation #3 (Central AZ)Canine Seroprevalence
Canine Serosurvey conducted in 2010: 14/276 (5.1%) of dogs were positive Index Community: 13 dogs positive Results helped tribe focus limited resources
on prevention efforts in the affected community No new human cases since 2009
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Reservation #3 (Central AZ)Canine Seroprevalence
Households with SFGR tested dog
Household with SFGR-positive dog
travel history
Index household
+
+
+
++
Reservation #3: Index Community and Positive Dogs
Reservation #4 (Southern AZ)First Human Cases: 2011
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Seroprevalence in Dogs from Reservation #4 (Southern AZ)
District Number of RMSF
Positive Dogs
Number of
Dogs Tested %
District A 11 21 53
District B 3 17 18
District C 3 18 17
District D 0 18 0
District E 0 19 0
District F 2 18 11
District G 1 18 6
District H 4 18 22
District I 57 109 52
District J 2 19 11
District K 2 19 11
Total 85 297 29
Reservation #4 (Southern AZ)
Canine Serosurvey conducted in 2011: 85/297 dogs positive (28.6%%) of dogs were positive
Numerous Communities positive, some > 50% seropositivty in dogs
Results informed tribe that focused efforts unlikely to be successful, efforts needed reservation-wide
Seroprevalence in Dogs from Non-Reservation Communities,
2005-2006
• 5.7% of dogs (n=14/247) were seropositive
• Dogs in counties directly bordering the affected area had higher rates
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Correlation between Canine Seropositivity and Human Risk
Seropositivity Rate and Human Risk In general, no human cases in communities where the canine
seropositivity rate is ~ 5%
Human cases observed in communities where canine seropositivity is > 50%
Threshold for human risk somewhere in between
Canine seropositivity has been observed prior to the first reports of human cases on some reservations
Seropositive dogs (>60%) reported in northern reservations, but no confirmed human cases Is human surveillance adequate?
First human case identified/reported does not equal the first human case
RMSF in Mexico
2009 urban outbreak in Mexicali, Mexico, near the U.S. border > 1,000 suspected cases
Children disproportionately affected
Rhipicephalus sanguineus the associated vector
Stray and free-roaming dogs an amplifying factor
RMSF cases have continued to be identified throughout much of Mexico, likely endemic
Origins of R. rickettsii in Rhipicephalus sanguineus Ticks
Strains of R. rickettsii circulating in AZ are distinct from strains circulating in Mexicali, Mexico Rhipicephalus ticks in eastern AZ are genetically different
than ticks from Mexicali
No evidence ticks were “imported” from Mexico
R. rickettsii strains in AZ distinct from strains associated with Dermacentor ticks in the western U.S. and eastern U.S.
Likely present at low enzootic levels in many areas
May emerge as an outbreak or epidemic under the right environmental conditions
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Climate and RMSF Risk
Bimodal seasonal peak (dip in early summer and peak in late summer/fall) suggests a correlation between human risk and moisture levels
Monsoon season June 15-September 30
Additional climactic analyses are needed to assess this observation
May provide advance recognition of higher risk tick years (heavy monsoon rains) and a point of intervention
Effects of climate change difficult to predict
Vectorborne diseases in general likely sensitive to climate change
Discussion
• Since its emergence in Arizona almost a decade ago, RMSF has become established as an enzootic focus and spread to new areas.
• Dogs play an important role in the ecology of RMSF in this region. Dogs may serve as sentinels for human risk, and help direct prevention efforts in affected communities.
• Control of dogs and ticks the key to control, but prevention is difficult due to limited resources, regional isolation, and huge tick/dog populations. Early detection and aggressive interventions are key to success.
Prevention Efforts
• Treat dogs for ticks all year (collars, topspots, dips, sprays)
• Treat environment for ticks (properly timed, successive months)
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Prevention Efforts
• Control dog population (spay/neuter)
• Change free-roaming culture tie/fence)
• Remove tick harborage (old mattresses, etc)
• Education
Prevention Efforts
RMSF Intervention Assessment: 2005
• 218 homes on Reservation #1 assessed for ticks between April 18-May 13, 2005
• Dry ice traps to quantify #’s of ticks (tick density)
• Re-assessed after spraying
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Tick Trapping Results, Pre-Intervention April 2005
Reservation #1
Community A
Community B
# houses assessed 57 161
# positive tick traps 23 (40%) 90 (56%)
Density (1-10 ticks) 19 (83%) 58 (64.5%)
Density (11-100 ticks) 3 (13%) 27 (30%)
Density (>100 ticks) 1 (4%) 5 (5.5%)
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Tick Trapping Pre-Intervention Assessment
• All subdivisions assessed
• % of subdivisions yielding positive traps– 69% of Community A subdivisions– 83% of Community B subdivisions
• Tick activity was generally widespread
Post-Treatment Tick Assessment
• April 25-28: Community A homes sprayed with pesticide
• May 9-13: Repeated tick assessments to measure effectiveness
• 45% decrease in ticks
Summary of 2005 Intervention Assessment
• Despite early season, tick activity was high • Pesticide application very effective at
reducing #’s of ticks • Single application not sufficient to control
problem– New eggs hatch out as season advances
– Incomplete coverage of pesticide– Introduction of new ticks from free-roaming dogs
– Pesticide active only ~ 3-4 weeks
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Why Isn’t it Working?
• Insufficient prevention activities (scale, timing)• Once a summer applications not enough to fix the
problem• Household and dog treatments need to be properly
timed and applied to provide sustained acaracidal activity
• Lack of focus on control of free-roaming dogs• Stray dogs less a problem than poorly cared
for/unrestrained pet dogs• Culture of not fencing/tying dogs
• No permanent veterinary services on most reservations • Rural Area Veterinary services only comes once a
year, people must take their dogs to them
Neighborhood Pilot Project, 2012
• One community on Reservation #2
• Spay/Neuter every dog
• Remove unowned dogs
• Provide a collar, license, leash, and tie-out stake for every dog
• Treat every dog for ticks
• Treat every house for ticks (sustained effort over the summer)
• EDUCATE HOMEOWNER
• Monitor for changes in human RMSF cases
Neighborhood Pilot Project, 2012
• Goal: Prove improvement in human health by improving the health of the pet population
• Partners– Petsmart Charities
– Bayer
– PetCo Charities
– CDC, Indian Health Service, AZ Dept. Health
– Tribal RMSF Task Force
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Acknowledgements
CDC staff (RZB/NCEZID, ONDIEH/NCEH)
Members of the RMSF Tribal Task Forces
AZ DOH
IHS
Numerous others at the state, federal, and tribal levels
Disclaimer:The findings and conclusions in this manuscript are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.